Method and device for detecting a leak in a heat exchanger, especially a plate-type heat exchanger

ABSTRACT

The invention relates to a device for detecting a leak between two circuits of a plate-type heat exchanger ( 1 ) provided with means for filling two circuits with fluid at a different pressure, characterized in that said device comprises automatic control means for the convergence of the pressure inside said circuits with respect to a given threshold, and means for signalling a leak when the automatic control means have detected the occurrence of said convergence.

The invention relates to a method and to a device for detecting a leakin a heat exchanger for fluids, particularly in a plate-type heatexchanger, of the type used for processing milk.

A heat exchanger comprises a first circuit in which a first fluid cancirculate, and a second fluid in which a second fluid can circulate, asignificant proportion of the first and second circuits being in closecontact to encourage heat exchange between the two fluids. Plate-typeheat exchangers consist of several sections of several bundles ofcorrugated plates assembled by joints and are well suited to lengthyheat exchanges (reference may for example be made to patent U.S. Pat.No. 6,116,332 for an example of a plate-type exchanger). It is obviouslyof capital importance that the fluids of the two circuits not be indirect communication and is therefore appropriate periodically to checkthat there are not leaks from one circuit to the other.

Numerous methods and devices for detecting leaks, making it possible toavoid systematic disassembly and inspection of all the plates of theexchanger have already been proposed.

For example, according to a method described in document WO 95/16900, asaline solution is injected into one circuit and water is injected intothe other, and measuring the conductivity of the water in the secondcircuit makes it possible to detect whether salt is passed from onecircuit to the other, that is to say whether there is a leak. If thereis, ultrasound inspection makes it possible to determine which plate isholed. Such a test takes time (generally about four hours) and has thedisadvantage of not being predictive, in that it gives no informationabout the quality of the joints.

According to patent U.S. Pat. No. 6,009,745, a solvent solution iscirculated through one circuit and a gas is circulated through theother; a differential pressure is established in the two circuits, andthe appearance of a deposit of solute at the location of any leaks isvisually observed. However, such a solution which requires visualinspection can hardly be used where leaks are hidden from sight.

According to patent U.S. Pat. No. 5,170,840, a solution of sulfamic acidis circulated through one circuit and a colored mixture of caustic sodaand potassium permanganate is circulated through the other, and thecolored leaks which may arise are observed. This solution has the samedisadvantage as the previous one.

There is also a method whereby each circuit of each section ispressurized, section after section, and the change in pressure isobserved, its pronounced drop in one circuit of one section indicatingthat there is a problem. Such a system is also time consuming to employ.

The object of the invention is to propose a new method (and theassociated operating device) for detecting leaks, which does not havethe disadvantages of the known methods and allows an exchanger to betested more quickly and more easily.

The invention achieves its goal by virtue of a method for detecting aleak between the two circuits of a plate-type exchanger, of the type inwhich each of the two circuits is filled with fluid at a differentpressure, characterized in that the change in pressure in the twocircuits is observed and in that a converging of the pressures observedin the two circuits below a certain threshold is automatically monitoredand in that a leak detected when said convergence has been detected issignaled. Advantageously, the difference between the two pressures isperiodically calculated and a leak is signaled when the difference dropsbelow a certain threshold.

The invention makes it possible to define several sections in the twocircuits according to the connections of the inlets/outlets of theplates of the exchanger, and tests several sections of the exchangersimultaneously.

Advantageously, the connections to be made with a hydraulic test moduleto simultaneously test said several sections are automaticallyindicated.

The device for detecting a leak between the two circuits of a plate-typeexchanger, of the type comprising means for filling each of the twocircuits with fluid at a different pressure, is characterized in that itcomprises means for automatically monitoring the convergence of thepressures in the two circuits with respect to a given threshold, andmeans for signaling a leak in function when the automatic monitoringmeans have noticed said convergence.

Advantageously, these monitoring means comprise means for measuring thedifferential pressure.

Advantageously, the device comprises a hydraulic module and anelectronic module which are separate, the hydraulic module comprising anumber of connections for connecting to a number of inlets/outlets ofthe plate-type exchanger so that several sections of the exchanger canbe tested simultaneously.

Advantageously, the electronic module contains software for exploitingthe pressure measurements determined at the connections of the hydraulicmodule.

Advantageously, the software indicates, on the basis of theconfiguration of the sections, which configuration is input as data,what connections are to be made at the connections in order to take themeasurements.

Thus, according to the present invention, the two circuits are filledwith fluid (and this fluid is preferably water, which has the advantageof not contaminating the circuits), the two circuits are pressurized inall sections at once, establishing a differential pressure therein, andany critical convergence of the pressure is observed in all the sectionsat once, by constant measuring of the pressure and by virtue of thesoftware that exploits the measurements. The software built into theelectronic module takes into account the configuration of theinputs/outputs defining the sections, and from this automaticallydeduces what connections need to be made for carrying out the test inthe various sections; it then, by observing the test results, is ablefrom this to deduce in which section or sections a leak has beendetected.

The advantage of the invention is that it is possible to operate at theworking pressure of the heat exchanger, thus making it possible todetect leaks under working conditions, or to perform a manufacturer testat a higher pressure (which makes it possible to increase to a pressurethat also allows the joints to be checked). It also allows microcracksto be observed by adopting a higher observation pressure. This gives thetest of the invention a predictive dimension. Given the speed of thetest, the test can also be repeated reversing the differential pressurein the two circuits so as to force the microcracks to open up at leastin one of the two directions, thus making it possible to detect certaintypes of unidirectional microcracks.

Other characteristics and advantages of the invention will becomeapparent from reading the description which will follow, with referenceto the attached drawings in which:

FIG. 1 is a schematic perspective view of the device of the inventionand, in particular, of the hydraulic and electronic modules,

FIGS. 2, 3 and 4 are schematic views of the electronic module from thefront, from the rear and from above,

FIGS. 5 and 6 are schematic views of the hydraulic module from thefront, from the rear and from above,

FIGS. 7 to 9 show examples of the screen that appears on the electronicmodule during a test,

FIGS. 10 and 11 are graphs of the curves of the pressure in the twocircuits of two sections of an exchanger, the first being normal, thesecond showing a leak.

FIG. 1 shows a section of a plate-type exchanger 1 consisting of asupporting structure 2 supporting bundles of plates with reliefs 3assembled side by side by joints and between them defining two adjacentcircuits with respective inlets 4, 5 and outlets 6, 7 accessible on onewall of the supporting structure 2. Each plate or bundle of plates hasits own inlets/outlets and the two circuits may form several sectionsdefined according to the connections chosen for the variousinlets/outlets of the plates within the exchanger.

The device of the invention is in the physical form of two modules, oneelectronic 10 and one hydraulic 20, each comprising a carriagesupporting or containing a certain number of apparatuses.

The electronic module 10 comprises a computer processing unit connectedto peripherals such as a screen 12 readable from above, a printer 13placed in a drawer, a keyboard 14 placed in a drawer and a panel 15 ofmeasurement, signaling or switching instruments.

The hydraulic module 20 comprises a tank 21 equipped with a pump drivenby a motor 22. A connection 23 allows the hydraulic unit to be connectedto a test fluid supply, advantageously a water supply. A connection box24 has various connections 25 which can be linked selectively by hoses26 equipped with couplings 27 to the inlets/outlets 4-7 (or others) ofthe section of the exchanger that is to be tested. In the exampledepicted, there are six pairs of connections 25 allowing thesimultaneous consideration of six exchanger sections. Each of the pairsof connections is linked, in the module, to a pressure sensor whichmakes it possible constantly to determine the pressure in the twocircuits of the various sections.

The software incorporated into the processing unit of the electronicmodule allows the configuration of the inputs/outputs defining thesections to be taken into consideration, for example in the formdepicted in FIG. 7 which shows one of the screens that appear during thetest. This screen shows the four plates 3 of the exchanger with theirinlets/outlets identified by a code. The table 30 shows precisely whatthe inlets/outlets of the three sections defined in this example are.

On the basis of this configuration input by the user by way of data, thesoftware deduces what connections need to be made in order to carry outthe test in the various sections and these connections are indicated bythe screen visible in FIG. 8, indicating where each of the hoses 26 ofthe hydraulic module need to be connected to.

Once these connections have been made, the test is initiated from theelectronic module, having beforehand set the desired pressure values.The test pressure is advantageously higher than the operating pressureto make sure that any cracks that are forming open up; for example, theformer is 5 to 15 bar whereas the latter is 3 to 10 bar. Thedifferential pressure to be established between the two circuits is alsoset, for example at between 2 and 5 bar, and the pressure hold is alsoset, for example to 20 minutes. The values of the pressure of the fluidin the two circuits of all the sections considered (for example threesections) are simultaneously and constantly measured (or are measured atclosely spaced intervals), thus making it possible for each section toestablish a graph of the two pressure curves. The softwaresimultaneously calculates the pressure difference between the two curvesfor each time interval and signals any appreciable convergence (that isto say any convergence below a predefined threshold), or any crossing ofthe curves by an indication that can be read on the screen, in boxes 31;if there is no critical convergence, that is also signaled. Buttons 32allow access to the graph itself, if so wished, this being of the typeshown in FIG. 10 or 11 which respectively represent the case where thereis no appreciable convergence and a case where there is criticalconvergence (and therefore leakage).

It can therefore be deduced from the results of the test that section 2of the exchanger has a leak.

1. A method for detecting a leak between the two circuits of aplate-type exchanger (1), of the type in which each of the two circuitsis filled with fluid at a different pressure, characterized in that thechange in pressure in the two circuits is observed and in that aconverging of the pressures observed in the two circuits below a certainthreshold is automatically monitored and in that a leak detected whensaid convergence has been detected is signaled, observation involvingperiodically calculating the difference between the two pressures, theleak being signaled when this difference drops below a certainthreshold.
 2. The method as claimed in claim 1, characterized in thatseveral sections are defined in the two circuits according to theconnections of the inlets/outlets of the plates of the exchanger (1),and in that several sections of the exchanger (1) are testedsimultaneously.
 3. The method as claimed in claim 2, characterized inthat the connections to be made with a hydraulic test module tosimultaneously test said several sections are automatically indicated.4. A device for detecting a leak between the two circuits of aplate-type exchanger (1), of the type comprising means for filling eachof the two circuits with fluid at a different pressure, characterized inthat it comprises means for automatically monitoring the convergence ofthe pressures in the two circuits with respect to a given threshold, andmeans for signaling a leak in function when the automatic monitoringmeans have noticed said convergence, said monitoring means comprisingmeans for measuring the differential pressure.
 5. The device as claimedin claim 4, characterized in that it comprises a hydraulic module (20)and an electronic module (10) which are separate, the hydraulic modulecomprising a number of connections (25) for connecting to a number ofinlets/outlets (4-7) of the plate-type exchanger (1) so that severalsections of the exchanger can be tested simultaneously.
 6. The device asclaimed in claim 5, characterized in that the electronic module (10)contains software for exploiting the pressure measurements determined atthe connections (25) of the hydraulic module (20).
 7. The device asclaimed in claim 6, characterized in that the software indicates, on thebasis of the configuration of the sections, which configuration is inputas data, what connections are to be made at the connections (25) inorder to take the measurements.